Various fixes (#444)

- Add missing symbols for TactilitySDK
- Disable display idle logic when there's no LVGL display

Tactility/Source/service/displayidle/DisplayIdle.cpp

@@ -25,13 +25,20 @@ class DisplayIdleService final : public Service {
         // Settings are now cached and event-driven (no file I/O in timer callback!)
         // This prevents watchdog timeout from blocking the Timer Service task
 
+        if (lv_disp_get_default() == nullptr) {
+            return;
+        }
+
         // Query LVGL inactivity once for both checks
         uint32_t inactive_ms = 0;
         if (lvgl::lock(100)) {
             inactive_ms = lv_disp_get_inactive_time(nullptr);
             lvgl::unlock();
+        } else {
+            return;
         }
 
+        // TODO: The following logic only works with the first display. There might be multiple displays.
         // Handle display backlight
         auto display = getDisplay();
         if (display != nullptr && display->supportsBacklightDuty()) {

TactilityC/Private/symbols/string.h

@@ -0,0 +1,5 @@
+#pragma once
+
+#include <private/elf_symbol.h>
+
+extern const esp_elfsym string_symbols[];

TactilityC/Source/symbols/string.cpp

@@ -0,0 +1,14 @@
+#include <private/elf_symbol.h>
+#include <symbols/string.h>
+
+#include <string>
+
+extern "C" void _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE15_M_replace_coldEPcjPKcjj(void*, char*, unsigned int, char const*, unsigned int, unsigned int);
+
+const esp_elfsym string_symbols[] = {
+    // Note: You have to use the mangled names here
+    { "_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE15_M_replace_coldEPcjPKcjj", (void*)&_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE15_M_replace_coldEPcjPKcjj},
+    // { "", (void*)&(std::) },
+    // delimiter
+    ESP_ELFSYM_END
+};

TactilityC/Source/tt_init.cpp

@@ -25,6 +25,7 @@
 #include "symbols/esp_http_client.h"
 #include "symbols/pthread.h"
 #include "symbols/stl.h"
+#include "symbols/string.h"
 #include "symbols/cplusplus.h"
 #include "symbols/freertos.h"
 #ifndef CONFIG_IDF_TARGET_ESP32P4
@@ -633,10 +634,11 @@ uintptr_t tt_symbol_resolver(const char* symbolName) {
 #endif
         stl_symbols,
         cplusplus_symbols,
-        esp_event_symbols,
-        esp_http_client_symbols,
         pthread_symbols,
         freertos_symbols,
+        string_symbols,
+        esp_event_symbols,
+        esp_http_client_symbols,
     };
 
     for (const auto* symbols : all_symbols) {